1. Field of the Invention
The present invention relates to a four-cycle engine for a small watercraft such as a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction.
2. Description of the Related Art
In recent years, small watercraft such as jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The jet-propulsion watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the jet-propulsion watercraft is propelled.
In the jet-propulsion watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
In the case of the jet-propulsion personal watercraft, which is one type of the small watercraft, recently, a four-cycle internal combustion engine (four-cycle engine) has been employed in place of a two-cycle internal combustion engine (two-cycle engine), as in the case of other small watercrafts.
In consideration of improvement in response and fuel consumption of the engine, in some cases, a fuel injection type engine which injects a fuel into an air-intake passage has been employed in recent small watercrafts.
In the case of the two-cycle engine of the fuel injection type engine, oil is mixed into a fuel itself. Therefore, oil is supplied to a valve such as a throttle valve provided in the air-intake passage and a valve stem thereof.
Meanwhile, in the case of the four-cycle engine, the oil is not contained in the fuel to be supplied.
Accordingly, when the four-cycle engine is employed, it is necessary to provide an oil supply port and an oil supplier having an electromagnetic valve in the vicinity of the valve in the air-intake passage for the purpose of supplying an oil, as disclosed in Japanese Laid-Open Patent Publication No. Hei 7-317520.
Actually, however, the oil itself is difficult to spread because of its high viscosity. Therefore, when the valve is provided in the vicinity of the oil supply port, the oil is sufficiently supplied, while when the valve is provided apart from the oil support port, the oil is not sufficiently supplied. Also, some engines are provided with a plurality of valves in the air-intake passage. In that case, the oil is sufficiently supplied to the valve positioned in the vicinity of the oil supply port, while the oil is not sufficiently supplied to the valve positioned apart therefrom.
The present invention addresses the above-described condition, and an object of the present invention is to provide a four-cycle engine for a small watercraft, capable of sufficiently supplying oil to a valve irrespective of the position of the valve in an air-intake passage, that is, the position of an oil supply port in the air-intake passage.
According to the present invention, there is provided a four-cycle engine for a small watercraft comprising: a fuel injector for injecting a fuel into an air-intake passage through an injection nozzle; an openable valve provided in the air-intake passage for regulating an intake amount of air into a cylinder; a fuel supply passage through which the fuel is supplied to the injector; and an oil supply passage connected to the fuel supply passage through forced oil supply means, wherein a proper amount of oil is supplied to the fuel supply passage by the forced oil supply means during engine running.
In the four-cycle engine for the small watercraft so constituted, the oil is mixed into the fuel and the resulting oil-fuel mixture is supplied from the fuel injection nozzle into the air-intake passage. Since the viscosity of the oil-fuel mixture is low as a whole, the oil is supplied to the valve regardless of whether the valve is positioned apart from or in the vicinity of the fuel injection nozzle. In addition, because of the low viscosity, the oil is also lubricated sufficiently to a narrow space around a valve stem. As a matter of course, since the oil is always supplied to the surface of the valve, the rustproof effect can be produced on the surface of the valve.
In the four-cycle engine for the small watercraft, it is preferable that the forced oil supply means includes an electromagnetic valve, and the electromagnetic valve is operated according to an engine speed, thereby changing an amount of oil supply according to the engine speed. With this constitution, when the engine speed is high and, therefore the amount of oil supply needs to be increased, a large amount of oil is supplied, while when the engine speed is low and, therefore, the amount of oil supply needs to be reduced, a small amount of oil is supplied.
In the four-cycle engine for the small watercraft, it is preferable that an open time of the electromagnetic valve is increased according to an increase in the engine speed. Otherwise, it is preferable that an opening of the electromagnetic valve is increased according to an increase in the engine speed.
In the four-cycle engine for the small watercraft, it is preferable that the oil is supplied in an oil-to-fuel volume ratio in a range of approximately 3:1000 to approximately 20:1000. Thereby, desired functions and effects can be obtained.
According to the present invention, even when the fuel injection type four-cycle engine is employed as the engine for the small watercraft, the oil is supplied to the valve irrespective of the position of the valve in the air-intake passage; that is, the position of the oil supply port in the air-intake passage.
As a result, since the oil is supplied to the valve in the air-intake passage and a portion provided around its stem, the rustproof effect and the lubricating function can be fulfilled. This facilitates the generalization of the fuel injection type four-cycle engine as the engine for the small watercraft.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.